The present application claims a priority of Japanese Patent Application No. 2001-60811 filed on Mar. 5, 2001 and is inserted herein.
The present invention relates to an improvement of a compensation mechanism for compensating an error of a measured coordinate position, in a moving machine having a coordinate space mechanism such as a Coordinate Measuring Machine, a machine tool, a robot and the like.
A position measuring apparatus which can execute a position measurement within a three-dimensional space has been used for executing an accurate operation, in various moving machines such as the Coordinate Measuring Machine, the machine tool, the robot and the like.
As the position measuring apparatus mentioned above, a description will be given by exemplifying the Coordinate Measuring Machine. In the Coordinate Measuring Machine, it is possible to determine a distance from a first target position to a second target position in a subject to be measured by measuring coordinates of the first target position and the second target position. If the manner mentioned above is continuously used, it is possible to accurately comprehend a two-dimensional or three-dimensional shape of the measured subject.
However, at a time of determining a coordinate of a target position, there is a case that a distortion is generated in a mechanical shape of the Coordinate Measuring Machine, for example, by moving a detector such as a contact-type probe or the like for detecting the target position. Accordingly, there has been a case that an error is occurred in indexing an accurate position coordinate. Therefore, in the conventional art, in order to prevent the distortion in the mechanical shape mentioned above, a countermeasure of increasing a static rigidity or the like has been employed.
Further, in order to measure an error included in the measured value, minimize a geometrical error and make it possible to correspond to a high accuracy, there has existed an apparatus which mounts a software for computing the geometrical error on the basis of the geometrical error measured by a reference device or the like and giving a compensation to the measured positional coordinate.
A key point in volumetric measuring accuracy correction of the Coordinate Measuring Machine is the geometrical error. Accordingly, a basic operation order of the software is shown by a block diagram in FIG. 5. As shown in FIG. 5, the software of this kind at first mounts a length reference device such as a gauge block or a step gauge, or an angle reference device such as a right angle reference device on a table of the Coordinate Measuring Machine. Then, a measurement is executed by setting these reference devices as a workpiece. Next, the geometrical error data are determined on the basis of these measured values, a command value of a position at a time of executing the measurement, the error of the reference devices themselves and the like. Then, ranges with appropriate length are determined by analyzing the error data. In each of the ranges, the errors are approximated in accordance with a function (data fit), thereafter, the errors are classified into respective error kinds at every axis in accordance with a kinematic model of the measuring apparatus, and a compensation parameter with respect to the measured coordinate is prepared. The parameter is stored and the compensation with respect to the measured coordinate is executed.
Since an influence of a reason such as the angle error or the like is generally included in the geometrical error measured in the Coordinate Measuring Machine, it is necessary to execute an isolation process of the error, in order to treat as the errors on the respective axis. In this case, the kinematic model is used for the isolation process of the errors. The geometrical errors isolated by using the kinematic model has three scale errors in a rectangular coordinates system each one being with respect to the respective axis, three errors in a straightness within a vertical plane each one being with respect to the respective axis, three errors in a straightness within a horizontal plane each one being with respect to the respective axis, three pitching errors each one being with respect to the respective axis, three yaw errors each one being with respect to the respective axis, three rolling errors each one being with respect to the respective axis, and three perpendicular errors between the respective axis (xy axis, yz axis and zx axis), and totally has twenty one errors. This kinematic model is used for isolation the errors at a time of computing the compensation parameter and at the same time, is used at a time of converting the respective compensation parameter into the errors on the coordinate space at a time of executing the compensation.
Even when the errors in the respective axis exist by using the process mentioned above, the geometrical error compensating capacity of the Coordinate Measuring Machine is improved by measuring and compensating the errors. Accordingly, it has been possible to achieve a high accuracy of the Coordinate Measuring Machine.
As mentioned above, in order to measure the accurate positional coordinate, it is important that a relation between the moving machine and the reference surface corresponding to the reference of the positional coordinate is kept constant. Among them, a guide for the moving machine provided on the reference surface has a particularly important role. Even when the high accuracy of the Coordinate Measuring Machine is realized by utilizing the space accuracy compensation in accordance with the software, a deterioration of accuracy in the Coordinate Measuring Machine is directly caused if the guide for the moving machine provided on the reference surface is changed due to a deterioration with age or a temperature fluctuation. Therefore, in the conventional art, in the same manner as mentioned above, a countermeasure is given by increasing the static rigidity and controlling the ambient temperature.
However, in recent years, there has appeared a large Coordinate Measuring Machine. With respect to the large apparatus mentioned above, as well as it is very hard to place a temperature-controlled chamber, the large apparatus directly uses a base as a reference surface in most cases. Accordingly, even when a building in which the temperature is controlled is completely provided, the base is changed largely between summer and winter. In accordance with the current space accuracy compensation, it has not been possible to secure a sufficient accuracy.
Further, even in the compact apparatus, since the deterioration with age of the base corresponding to the reference surface is generated even if it is a very little, it can not be ignored for the purpose of aiming a further high accuracy.
The present invention is made in consideration of the problems mentioned above, and a first object of the present invention is to provide a position measuring apparatus which can execute a stable accuracy assurance at a high accuracy against a deterioration with age and a temperature fluctuation of the apparatus while making a correction of an existing volumetric measuring accuracy effective. Further, a second object of the present invention is to provide apparatus which can execute a further accuracy stability and improve a reliability while keeping a general-purpose property even in a Coordinate Measuring Machine.
In order to achieve the object mentioned above, in accordance with the present invention, there is provided a position measuring apparatus comprising:
a position coordinate measuring mechanism constituted by a target position detector, a moving machine and a positional coordinate computer;
a memory classifying geometrical errors on the basis of a positional coordinate measured by the position coordinate measuring mechanism and storing compensation parameters determined from the respective classified errors;
an error compensator for reading out the compensation parameters so as to compensate the errors; and
the target position within a specified coordinate space being measured on the basis of a coordinate system,
wherein the position measuring apparatus comprises:
a detector for measuring whether or not a change is occurred in a relation with respect to a reference surface, in a movement executed by the moving machine; and
an error corrector for correcting any one of the compensation parameter compensating the positional coordinates at least by the error compensator and the positional coordinate compensated by the error compensator in order to remove an influence given to the positional coordinate computed by the positional coordinate computer in correspondence to the relation between the movement executed by the moving machine and the reference surface, on the basis of an amount of change of the relation measured by the detector, in the case that the change is occurred.
In this case, the target position detector detects the target position in the coordinate space with respect to a predetermined reference surface.
Further, the moving machine moves in accordance with a predetermined relation with respect to the reference surface for the purpose of detecting the target position by the target position detector so as to move the target position detector.
The positional coordinate computer computes the target position from the data such as the displacement of the moving machine.
Further, in the position measuring apparatus in accordance with the present invention, it is preferable that the coordinate system is an xyz rectangular coordinates system in which the coordinate system is extended in vertical, horizontal and height directions.
Further, in the position measuring apparatus in accordance with the present invention, it is preferable that the moving machine comprises:
a horizontal direction moving machine for moving in conformity with or in parallel to an x axis;
a vertical direction moving machine for moving in conformity with or in parallel to a y axis; and
a height direction moving machine for moving in conformity with or in parallel to a z axis,
and the detector is provided in any one of the vertical direction moving machine, the horizontal direction moving machine and the height direction moving machine.
Further, in the position measuring apparatus in accordance with the present invention, it is preferable that the detector is constituted by a reference side angle meter and a measurement side angle meter.
Further, in the position measuring apparatus in accordance with the present invention, it is preferable that the moving machine comprises:
a vertical direction moving machine constituted by a straight guide provided on the reference surface and vertical direction moving mechanism capable of moving along the guide;
a horizontal direction moving machine constituted by a straight guide mounted to a top of the vertical direction moving machine and provided in a direction parallel to the reference surface and orthogonal to the movement direction of the vertical direction moving machine, and a horizontal direction moving mechanism moving along the guide; and
a height direction moving machine constituted by a rod-liked member mounted to the horizontal direction moving machine and provided with the target position detector at a tip, and a height direction moving mechanism moving the rod-liked member in a direction orthogonal to the reference surface;
the vertical direction moving machine moves the target position detector on a specified straight line on the reference surface,
the horizontal direction moving machine moves within a surface orthogonal to the movement direction of the vertical direction moving machine and in parallel to the reference surface,
the height direction moving machine has a predetermined relation with respect to the reference surface by moving in a direction orthogonal to the reference surface, and
the detector is constituted by a reference side angle meter provided on a guide of the vertical direction moving machine and a measurement side angle meter provided in the vertical direction moving mechanism.
Further, in the position measuring apparatus in accordance with the present invention, it is preferable that the angle meter is a biaxial angle level.
Further, in the position measuring apparatus in accordance with the present invention, it is preferable that the angle meter is a laser angle level.
Further, in the position measuring apparatus in accordance with the present invention, it is preferable that the coordinate system is a biaxial rectangular coordinates system.
Further, in the position measuring apparatus in accordance with the present invention, it is preferable that an amount of change of the relation measured by the detector includes a pitching error and a yaw error with respect to an axis in a specified linear direction.
Further, in the position measuring apparatus in accordance with the present invention, it is preferable that a memory for saving an amount of change of the relation measured by the detector is further provided, and the detector is detachably provided.
Further, in order to achieve the object mentioned above, a working apparatus in accordance with the present invention has a feature that the position measuring apparatus in accordance with the present invention is provided.